This invention relates to a circular cam ring assembly for use in controlling the reciprocal movements of yarn engaging sinker elements in a circular knitting machine. This invention also relates to the individual cam segments which are affixed to the cam ring so as to form a generally circular race having repetitive, wave-like variations which cause the sinkers to reciprocate as they travel around the race.
Broadly speaking, circular knitting machines for knitting jersey, terry cloth materials and the like have long been known and used in the prior art. Such machines typically include a sinker cam assembly having a stationary circular cam ring and a rotatable sinker ring disposed coaxially and in registry with the cam ring. The sinker ring contains a plurality of circumferentially spaced apart, radially extending slots which open onto a broad surface thereof so as to face the cam ring. A like plurality of yarn engaging sinkers are slidably disposed in the slots for repetitive, radially inward and outward movement to engage a thread of yarn, carry the yarn into engagement with a needle, and thereafter retract so that the yarn engaged needle can complete a stitch.
A series of individual cam segments are attached to the cam ring so as to form a pair of radially spaced apart, inwardly and outwardly facing cam surfaces forming a generally circular closed path or race around the cam ring which contains repetitive, wavelike variations. The sinkers each contain a pair of spaced apart axially extending arms which ride along these cam surfaces as the sinker ring rotates. The wavelike variations or undulations in the cam surfaces thus cause the sinkers to reciprocate in radial directions in their slots as the sinker ring rotates.
A difficulty encountered in using these prior art cam ring assemblies is caused by the gaps which exist between adjoining pairs of cam segments. As a given radially extending sinker crosses the gap that exists between adjoining cam segments, centrifugal force caused by rotation of the sinker ring urges the sinker to move outwardly in its slot so that the radially inwardly located sinker arm moves into the inwardly opening end of the gap. As the sinker ring continues to rotate such that the sinker crosses the gap, the radially inwardly located arm tends to strike a leading edge portion of the inwardly facing cam surface of the next succeeding cam segment with a glancing blow. During each revolution of the sinker ring, a given sinker will thus strike the leading edge portion of that cam surface of the various cam segments as many times as there are gaps in the cam ring.
Accordingly, the individual sinkers are subjected to many glancing blows during each revolution of the sinker ring, all of which produces wear and damage to the sinkers, which necessitates frequent down time for replacement of the sinkers. Moreover, these glancing blows of the many sinkers in a given sinker ring against each of the cam segments causes wear and damage to the relatively more expensive cam segments which, likewise, necessitates down time and replacement of the cam segments, which is a substantially greater expense than that of replacing the sinkers.
In some types of circular knitting machines, this problem has been dealt with by using relatively long arcuate cam segments so that relatively few segments, and, therefore, relatively few gaps between adjoining segments, exist around a cam ring. Accordingly, the sinkers encounter fewer gaps with each revolution of the sinker ring about the cam ring and thus encounter fewer jolts and glancing blows per revolution. Also, the straight ends of these prior art cam segments are sometimes tapered so as to be at an oblique angle relative to a radius of the sinker and/or cam ring which is drawn through either end of the gap between adjoining segments, so that the sinker will not tend to drop into the gap and thereby encounter a tearing, bending or otherwise deforming jolt when crossing the same. See, for example, U.S. Pat. No. 4,040,276 issued to R. A. Koegel on Aug. 9, 1977.
But some types of knitting machines are not adapted for using relatively long arcuate cam segments because of the numerous specific knitting operations to be performed during each revolution of the sinker ring, so that there is still a great need to use a cam ring assembly having a large number of relatively small cam segments. Since these small prior art cam segments are typically steel castings, there is a relatively wide range of dimensional variations between the largest and smallest ones in a given set such that they can not be closely fit end-to-end, whereby they contain relatively wide gaps between adjacent pairs when affixed to a cam ring.
By means of our invention as herein disclosed, these and other difficulties encountered using sinker cam assemblies in knitting machines of the prior art are substantially reduced, if not altogether eliminated.